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Revisiting Long Duration Winter Peak Events in the Southeast

image credit: Southern Alliance for Clean Energy, Seasonal Electric Demand in the Southeast
John Wilson's picture
Research Director, Resource Insight, Inc.

I have worked on utility regulation for the past 13 years. Areas of focus include:- Utility energy resource planning and procurement- Rate reform to address energy efficiency and distributed...

  • Member since 2007
  • 50 items added with 25,997 views
  • Feb 26, 2021

Last year, a report I co-authored examined what we termed "Long Duration Winter Peak Events." Part of a report on "Seasonal Electric Demand in the Southeastern United States," we took an in-depth look at two decades of hourly load data from 22 utility systems.

I am sure that many people are looking at the blackouts in Texas, Louisiana and Arkansas, the significant damage to those electric grids, and the economic fallout with worry. Could that happen to my utility?

Which Southeastern utilities have the most frequent long duration winter peak events?

Across the Southeast, for most utilities, winter peaks are of shorter duration than summer peaks. However, the most strongly winter peaking systems also have occasional long duration peak events of 14 hours or more and, more rarely, exceeding 20 hours. The four utility systems with the most history of long duration winter peaks all have substantial membership from rural electric cooperatives:

  • Santee Cooper (SC)
  • Seminole Electric Cooperative (FL)
  • PowerSouth (AL)
  • Tennessee Valley Authority (TN and six adjacent states)

These four cooperative systems supply much or all of the generation to their member utility systems.

Over a two-decade period, four other Southeastern utility systems had a few long duration winter peak events, and the remaining 14 had two or fewer events.

Are long duration winter peak events becoming more common in the Southeast?

Probably not. The historical frequency and severity of long duration winter peak events is probably a good proxy for the potential risk of extreme winter grid stress. We found that even though winter peak variability is higher than summer peak variability, there is no evidence of an increase or decrease to seasonal peak variability. This suggests that systems that haven't had long duration peak events are unlikely to have such events in the future.

Can utilities prevent blackouts during long duration winter peak events?

Utilities can winterize their coal and gas generation plants, but that doesn't guarantee reliability during the most severe events. In 2018, Duke Energy reported that even though it had made investments and improvements in freeze protection following outages at coal and gas plants in the winters of 2014 and 2015, the additional freeze protection would not entirely remove the potential for higher outage rates. In a regulatory filing, Duke Energy explained the risk of outages at coal and gas plants as follows:

"In particular, during extreme weather, customer demand is very high which results in the system's oldest and least efficient units running for longer durations than they would under normal conditions. As a result, outage rates greater than seasonal average outage rates ... would be expected."

For the four utility systems listed above, I'm not aware of any public reviews of how well prepared they are for extreme winter events.

Of course, blackouts don't just occur in wintertime. A new report from Berkeley Lab on the economic impacts of extreme weather events on utility systems includes a case study on FPL's response to hurricanes Katrina and Wilma. For much of the Southeast, wintertime is when the risk of power outages and the resulting hardships is at its least worrisome level.


Matt Chester's picture
Matt Chester on Feb 26, 2021

Quite timely indeed, and interesting to see where you were going with this piece before the fiasco on ERCOT. I'm wondering if anything you observed happening in Texas in the past few weeks provides new insights or unexpected data points or if everything more or less went how you would have anticipated given the series of events? 

John Wilson's picture
Thank John for the Post!
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